This invention relates to a tape position detecting device which is suitable for detection of the position of a magnetic tape, for instance, in a cuing operation with a video tape recorder.
In the case where signals are to be recorded on a magnetic tape or reproduced therefrom with a video tape recorder, it is necessary to detect a magnetic tape position; that is, it is necessary to perform a so-called "cuing operation". For this purpose, there are available a variety of tape position detecting devices employing various tape position detecting methods.
A first tape position detecting method is as follows: As shown in FIG. 1, a time code track TC is formed on a magnetic tape 1 in a longitudinal direction, and a time code LTC representing the absolute position of a record track TR on the magnetic tape 1 using, for instance, hours-minutes-seconds and frame number is recorded on the time code track TC. In the cuing operation, the time code LTC is reproduced from the track TC to detect the tape position.
A second tape position detecting method is as follows: A time code VITC including hours-minutes-seconds and a frame number is superposed on the vertical flyback time part of the video signal recorded on a record track TR of the magnetic tape 1, instead of the time code track TC. In the cuing opertion, the time code VITC is separated from the signal which is reproduced from the record track TR, to detect the tape position.
In a third tape position detecting method, the time code is not used, and instead means for mechanically detecting an amount of movement of a magnetic tape (hereinafter referred to as "tape movement detecting means", when applicable) by utilizing a capstan for driving the magnetic tape, a reel frequency signal, or a timer roller provided for this purpose only is employed to detect a relative tape position of the magnetic tape 1.
In the third tape position detecting method, sometimes a so-called "CTL timer" is employed. That is, CTL pulse signals recorded regularly on the control track CT formed longitudinally on the magnetic tape 1 are utilized to increase the accuracy of detection of the tape movement detecting means.
In practice, as shown in FIG. 2, a magnetic tape 1 is supplied from a supply reel 2A in a tape cassette 2, and is wound on a drum 6 with the aid of first and second inclination guide after passing through a guide pin 3A, a tension regulator pin 4, and a guide pins 3B, 5A and 5B. Thereafter, the magnetic tape 1, while being abutted against a time code recording and reproducing TC head 7 and a control track recording and reproducing CTL head 8 and engaged by a capstan 9A and a pinch roller 9B, is moved on, so that it is wound on a take-up reel 2B while being guided by guide pins 3C and 3D. Thus, the magnetic tape 1 supplied from the tape cassette 2 has been loaded in the tape recorder.
Under this condition, in the first tape position detecting method, the time code LTC is recorded on and reproduced from the time code track TC of the magnetic taped 1 with the TC head 7.
In the second tape position detecting method, the time code VITC is recorded on and reproduced from the record track TR of the magnetic tape 1 with rotary heads 6A and 6B positioned over the drum 6.
In the third tape position detecting method, the CTL pulse signal is reproduced with the CTL head 8, and frequency signals obtained from the capstan 9A and the reels 2A and 2B are applied to the tape movement detecting means.
The first and second tape position detecting methods using the time codes LTC and VITC recorded on the magnetic tape 1 are advantageous in that the absolute position of the magnetic tape 1 can be detected with high accuracy. However, the methods are still disadvantageous in that, since the operator can specify the time code LTC or VITC, the continuity of the time code LTC/VITC is not assured, and sometimes it is impossible to detect the relative position of the magnetic tape 1.
In addition, the methods give rise to another problem that, during the ordinary operation in which reproducing signals can be positively obtained from the magnetic tape 1, the absolute position of the magnetic tape 1 can be detected with high accuracy, but in the case where the magnetic tape 1 is subject to high speed signal reproduction or low speed reproduction, the time code itself cannot be reproduced with the result that the tape position of the magnetic tape 1 cannot be detected.
The tape position detecting methods cannot be employed at all in the case where the time code LTC/VITC has not been recorded on the magnetic tape 1.
In the third tape position detecting method using the so-called "CTL timer", it is impossible to detect the absolute position of the magnetic tape 1 since no means for detecting an absolute position is provided.
On the other hand, the absolute position of the magnetic tape 1 may be erroneous because of the slip of the capstan 9A or the reel 2A or 2B or because of an error in reading the CTL pulse signal; however, it may be detected no matter when signals are not recorded on the magnetic tape or no matter how the operating condition is.
In view of the foregoing, a tape position detecting device employing a fourth tape position detecting method has been proposed in the art. In the fourth tape position detecting method, during the ordinary operation, tape position data is detected using the time code LTC/VITC recorded on the magnetic tape 1; and in the case where the time code LTC/VITC cannot be obtained because signals have not been recorded on the magnetic tape 1 or because the operating condition is not suitable, the time code LTC/VITC is interpolated with the output value of the CTL timer, thereby to detect the tape position data.
In the tape position detecting device thus constructed, the output value of the CTL timer is an auxiliary value as a general rule. Therefore, with the timing that the time code LTC/VITC is read, instead of the tape position data interpolated with the output value of the CTL timer, a value corresponding to the time code LTC/VITC thus read is outputted as correct tape position data.
As a result, in the case where, as shown in FIGS. 3A and 3B, a record region PRN of ten minutes in which no time code LTC/VITC is recorded is present between a record region PRA of ten minutes (from 10 minutes to 20 minutes) and a record region PRB of five minutes (from 50 minutes to 55 minutes) in which the time code LTC/VITC are recorded, two substantially different values of tape position data may be arrived at for the same position on the magnetic tape 1. This fact adversely affects the cuing operation.
As shown in FIG. 3C, the output value CTL.sub.FW provided by the CTL timer when the cuing operation is carried out with the magnetic tape in the forward direction is a time of ten minutes (from 10 minutes to 20 minutes) in correspondence to the time code LTC/VITC when the record region PRA is subjected to reproduction; and then is a time of twenty minutes to twenty-nine minutes and fifty-nine seconds with the ten minutes interpolated when the record region PRN is subjected to reproduction. Thereafter, the output value is renewed with the timing that the reproduction of the record region PRB is started, so that it is a time of five minutes (from 50 minutes to 55 minutes) corresponding to the time code LTC/VITC.
In contrast, as shown in FIG. 3D, the output value CTL.sub.RW provided by the CTL timer when the cuing operation is carried out with the magnetic tape in the reverse direction has a value of five minutes (from 55 minutes to 50 minutes) corresponding to the time code LTC/VITC when the record region PRB is subjected to reproduction; and then has a value of fifty minutes to forty minutes one second with the ten minutes interpolated when the record region PRN is subjected to reproduction. Thereafter, the output value is renewed with the timing that the record region PRA is subjected to reproduction, so that it has a value of ten minutes (from 20 minutes to 10 minutes) corresponding to the time code LTC/VITC.
As is apparent from the above description, the value of the CTL timer, which is provided by interpolation of the record region PRN of ten minutes in which no time code LTC/VITC is recorded, shows different values--twenty minutes to twenty-nine minutes and fifty-nine seconds, and fifty minutes to forty minutes and one second--depending on the cuing directions. Hence, it is impossible to correctly detect the tape position data for cuing.
Furthermore, even in the case where the time code LTC/VITC on the magnetic tape can be read without fail, the continuity of the time code LTC/VITC is not assured. Hence, in order to perform the cuing operation correctly at all times, it is essential that the time code LTC/VITC is provided on the magnetic tape 1 in correspondence to the aimed tape position, and with respect to the direction of movement of the magnetic tape 1 the time code LTC/VITC increase or decrease monotonously. Thus, the conventional tape position detecting device is still insufficient in practical use.
The above-described difficulties may be eliminated by employing the third tape position detecting method in which the value of the CTL timer is utilized for the cuing operation. However, since the CTL timer employs mechanical detecting means to detect tape position data, the error due to the expansion of the magnetic tape 1 or the slip of the magnetic tape 1 on the capstan 9A cannot be prevented.
An additional problem is that, since only the CTL pulse signal is employed, the absolute position data of the magnetic tape 1 cannot be detected, and the detection error of the CTL pulse signal is accumulated. Thus, the method is inferior in the accuracy of tape position data than the above-described tape position detecting methods.
Furthermore, in the case where the magnetic tape 1 is moved repeatedly in the forward direction and in the reverse direction, the detection of tape position data is lowered in accuracy. Thus, the conventional methods are not sufficiently effective in solving the above-described problems.